Gear rolling

ABSTRACT

SINCE FORMING GEARS BY ROLLING, PARTICULARLY FROM THE SOLID, TENDS TO DISPLACE MATERIAL LATERALLY AT THE ENDS OF THE TEETH BEYOUND THE SIDE OF THE BLANK, THE ENDS OF THE ROLLED TEETH MAY NOT BE FULLY FORMED. TO CONTERACT THIS THE BLANK HAS TEETH PARTIALLY FORMED THEREON TO PROVIDE EXCESS MATERIAL ADJACENT THE ENDS OF THE TEETH.

Sept. 20, .1971 R. A. OKRAY 3,605,468

GEAR ROLLING Filed Aug. 4, 1969 v I VINVENTORS RAYMOND YA. OKRAY AT TORNEYS United States Patent 3,605,468 Patented Sept. 20, 1971 3,605,468 GEAR ROLLING Raymond A. Okray, Detroit, Mich., assignor to Lear Siegler, Inc., Santa Monica, Calif. Filed Aug. 4, 1969, Ser. No. 847,213 Int. Cl. B21h /02 US. Cl. 72-108 3 Claims ABSTRACT OF THE DISCLOSURE Since forming gears by rolling, particularly from the solid, tends to displace material laterally at the ends of the teeth beyond the side of the blank, the ends of the rolled teeth may not be fully formed. To counteract this the blank has teeth partially formed thereon to provide excess material adjacent the ends of the teeth.

BRIEF SUMMARY OF THE INVENTION There has recently been a revival of the practice of finishing gears by rolling them in mesh with hardened gear-like dies and this has been extended to producing gears by a rolling operation from a solid cylindrical blank or a blank in which teeth are partially formed. A present practice which is widely employed comprises rolling the gear or the gear blank between two opposed gear-like rolling dies and causing the dies to move radially inwardly to displace metal from the teeth of the gear or to form tooth spaces in the blank.

In either case there is a marked tendency for the metal as it is displaced by rolling contact with the teeth of the die to flow laterally beyond the sides of the blank with the result that the ends of the teeth formed or finished by this rolling process are in some cases not fully filled or formed to the required dimensions.

In order to overcome this ditficulty it is proposed to form the gear so that the teeth or portions of the teeth as provided thereon prior to the rolling operation have excess material adjacent the ends of the teeth.

Conveniently, this may be accomplished by hobbing the gear teeth on the blank or hobbing partially formed gear teeth on the blank in an operation characterized by a plunge feed without normal traverse between the gear and hob. Alternatively, if this operation with a particular diameter hob produces too much material adjacent the ends of the teeth, the operation may include limited relative traverse while the hob contacts the blank intermediate its sides in order to control the extra material provided adjacent the ends of the gear teeth.

Alternatively, the hobbing operation may be accompanied by relative traverse between the gear and hob to extend the cutting action from one side of the blank to the other but this traverse is further accompanied by a radial in and out feed so that more material is removed from the blank adjacent its mid-plane than adjacent the ends thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary diagrammatic view illustrating the condition of a rolled gear as compared to the desired form.

FIG. 2 is a fragmentary sectional view on the line 2--2, FIG. 1.

FIG. 3 is a plan view of the gear tooth illustrated in FIG. 2.

FIG. 4 is a diagrammatic sectional view illustrating the form of a gear tooth on a blank prior to rolling.

FIG. 5 is a plan view of the gear tooth shown in FIG. 4.

FIG. 6 is a view similar to FIG. 4 illustrating a modified tooth form.

FIG. 7 is a plan view of the tooth shown in FIG. 6.

DETAILED DESCRIPTION When gear teeth are formed from a solid blank or are finished by a rolling operation in which substantial material is moved by the rolling pressure developed between the teeth of the rolling die or dies and the blank, the displaced material of course moves in the path of least resistance. Accordingly, as the ends of the teeth are formed, the displaced material flows not only radially outwardly into the new tooth form, but also longitudinally of the tooth beyond the sides of the blank. It has been found that in many cases this results in teeth on the finished gear which are of reduced height and/or thickness adjacent the ends, or which may be said to have failed to fill adjacent the ends of the teeth.

In present practice it is contemplated that the gear teeth prior to the rolling operation will be partially formed by a cutting operation. Where the rolling operation is strictly a finishing operation, the gears are cut so as to leave a few thousandths of an inch of material which is then displaced by pressure generated between the teeth of the gear and the teeth of a pair of opposed rolling dies.

Where the rolling operation is effective to displace substantially more metal, the operation is not considered to be a finishing operation but as a roughing or final roughing operation. In this case the teeth are partially formed by a cutting operation such for example as breaching, hobbing, shaping or the like.

Referring first to FIGS. 1-3 there is illustrated in full lines the shape of a desired gear tooth 10, the tooth usually having uniform cross-section from end to end although it may in some cases be somewhat reduced at the ends in the form of crowned gear teeth familiar in the art. However, due to the fact that the material of the gear blank is not fully confined during the operation, it is found that adjacent the ends of the teeth material flows outwardly beyond the sides 12 of the blank as indicated at 14, and accordingly, the teeth do not fully fill either at the tops thereof as indicated by the dotted lines at 16, or on the sides thereof, as indicated by the dotted lines at 18. As a result of this, a tooth as viewed from the end has a central portion as seen in FIG. 1, which conforms to the desired form illustrated in full lines while the ends of the teeth are reduced either in height or thickness, or both, as indicated by the dotted lines.

It is found that undesirable results can be largely overcome by forming substantially fully formed or any partially formed teeth by an operation which leaves excess material adjacent the ends of the teeth in the blank.

Referring to FIG. 4 there is shown a fragmentary section of a blank 20 having teeth 22 which are of increased depth as indicated at 24 centrally thereof and which are of lesser thickness as indicated at 26 centrally thereof as compared to the ends.

A blank having teeth of this form may conveniently be produced by a hobbing operation in which a hob of predetermined diameter is employed in a hobbing operation characterized by a plunge feed in which no traverse axially of the blank is provided between the blank and the hob. It will be appreciated that the shape of the teeth resulting from this operation will be determined largely by the size of the hob and accordingly, the excess material left adjacent the ends of the teeth may be predetermined by selecting a hob of appropriate size.

Since excess material is thus provided adjacent the ends of the teeth, the displacement of material beyond the sides of the blank which results from the rolling operation will not result in reduction of the size of the end portions of the finished teeth.

After the rolling operation the material displaced beyond the sides of the blank can be removed by any suitable machining process.

While it is possible to predetermine the excess material provided adjacent the ends of the blank teeth for the purpose described by selecting the diameter of the hob, it is in many cases more convenient to employ a hob of smaller diameter and to provide limited axial traverse centrally of the blank. This has the result of forming teeth as illustrated in FIGS. 6 and 7 where the portions of the teeth 30 intennediate the lines 32 and 34 are of uniform cross-section, whereas only the end portions 36 and 38 are of increasing size.

Instead of providing an operation in which the hob is plunged into the blank or the operation in which it is given a limited axial traverse for a distance less than the width of the blank, it is also possible to produce a tooth formation as illustrated in FIGS. 4 and 5 by a hobbing operation in which the hob is traversed axially of the blank for a distance equal to the width of the blank and on this axial traverse is superimposed a gradual in and out feed so as to produce a greater depth of cut centrally of the teeth than adjacent the ends thereof.

What I claim as my invention is:

1. The method of rolling gears which comprises forming a blank with teeth having excess material to be displaced by a rolling operation between a pair of opposed gear-like rolling dies with their axes parallel to the axis of the blank, which comprises initially forming the teeth on the blank of longitudinally concave configuration to provide excess material adjacent the ends of the teeth, rolling the blank in pressure contact with the dies, and feeding the dies radially inwardly of the blank to desired depth to displace material into the final desired gear form from end to end of the teeth between the sides of the blank and to displace some excess material laterally beyond the sides of the blank.

2. The method as defined in claim 1 which comprises References Cited UNITED STATES PATENTS 3,362,059 1/1968 Di Ponio et al 29-159.2

LOWELL A. LARSON, Primary Examiner US. Cl. X.R. 

